Rocky mountain spotted fever

Background

  • Most frequent rickettsial disease reported in the US.[1]
  • Caused by Rickettsia rickettsii
    • Obligate intracellular, gram negative bacteria
    • Predilection for vascular endothelial cells
  • Spread by ticks
    • American Dog Tick (Dermacentor variabilis) Most common vector
    • Rocky Mountain Wood Tick (Dermacentor andersoni)
    • Brown Dog Tick (Rhipicephalus sanquineus)
    • Cayenne Tick (Amblyomma cajennense)
  • Seasonal distribution with most infections occurring in the summer months
  • Widely distributed in the US
    • States with the highest incidence are Oklahoma, Nebraska, Arkansas, Tennessee and North Carolina
  • Overall incidence is increasing while mortality is falling

Clinical Features

  • Symptoms generally begin 2-14 days after inoculation from an infected tick[2]

Early symptoms

  • Non specific and highly variable
  • Fever
  • Nausea/Vomiting
  • Abdominal pain
  • Myalgias (severe calf pain)
  • Headache
  • Fatigue
  • Conjunctivitis

Late symptoms

  • Arthralgias
  • Rash
    • Begins as a blanching maculopapular rash that evolves to become a petechial rash
    • Usually 2-5 days after fever subsides
    • Starts on extremities and spreads inward (centripetally)
    • Can involve palms and soles (50% of cases)
  • Positive Rumpel-Leede test
    • Development of petechiae at the site of blood pressure cuff and distally after compression

Complications

  • Secondary to host response against infected endothelial cells

Differential Diagnosis

Lower Respiratory Zoonotic Infections

Tick Borne Illnesses

Evaluation

  • PCR (initially)
  • Serial serologic examinations by indirect fluorescent antibody confirm the diagnosis
  • Titers

Work-Up

Management

  • Doxycycline 100 mg BID for 5-7 days[3]
    • Indicated also in children at 2.2mg/kg BID
  • Chloramphenicol (CAM) 50-100 mg/kg/day div Q6hr (Max dose = 4g/day)
    • Preferred agent in pregnancy. May cause aplastic anemia and Grey baby syndrome, more common in near term or 3rd trimester[1]
    • Consideration should be made for doxycycline over CAM in the 3rd trimester

Disposition

See Also

References

  1. 1.0 1.1 http://www.cdc.gov/rmsf/
  2. http://www.mayoclinic.com/health/rocky-mountain-spotted-fever/DS00600
  3. Shandera WX, Roig IL: Viral & Rickettsial Infections, in Papadakis MA, McPhee SJ (eds): Current Medical Diagnosis and Treatment, ed 52. USA, McGraw-Hill, 2013, (Ch) 32: p 1412-1413.